Voltage-based fuel gauge on battery capacity

ABSTRACT

A device to determine a state of a battery is disclosed. One or more transistors provide a resistance between first and second nodes. The one or more transistors are configured to conduct a supply current from a battery between the first node and the second node. A measurement circuit measures the voltage generated between the first node and the second node. The measurement circuit further measures the supply voltage. A calculation circuit generates an estimate of the supply current based on the voltage measured between the first node and the second node and the resistance of the one or more transistors. The calculation circuit generates an estimate of the state of charge of the battery based on the measured supply voltage and the estimate of the supply current.

TECHNICAL FIELD

This document pertains generally, but not by way of limitation, tobattery gauge circuits.

BACKGROUND

Battery gauges or monitors include electronic circuits that estimate thecurrent power level or capacity of batteries. An estimate of the currentpower level or capacity can be generated based, in part, on measuringthe voltage provided by a battery. For example, if the battery providesa relatively large supply voltage, then the supply voltage can indicatethat the battery has a significant portion of capacity remaining.Estimates of the remaining capacity of the battery can be useful foroptimizing the system efficiency or regulating the supply power.Moreover, the remaining capacity is relevant information forapplications that draw power from the battery, as well as applicationsthat charge the battery.

Overview

The systems, methods, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention as expressed bythe claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection titled “Detailed Description,” one will understand how thefeatures of this invention provide advantages that include improvingvoltage sensing.

In one example embodiment, a device to determine a state of a battery isdisclosed. The device comprises first and second nodes. The first nodeis configured to receive a supply current and a supply voltage from thebattery. The device further comprises one or more transistors configuredto provide a resistance between the first and second node. The one ormore transistors are configured to conduct the supply current betweenthe first node and the second node, thereby generating a voltage betweenthe first node and the second node. The device further comprises ameasurement circuit configured to measure the voltage generated betweenthe first node and the second node. The measurement circuit is furtherconfigured to measure the supply voltage. The device further comprises acalculation circuit configured to generate an estimate of the supplycurrent based at least on the voltage measured between the first nodeand the second node and the resistance of the one or more transistors.The calculation circuit is further configured to generate an estimate ofthe state of charge of the battery based at least on the measured supplyvoltage and the estimate of the supply current.

In another example embodiment, a method for determining a state of abattery is disclosed. The method comprises receiving, at a first node, asupply current and a supply voltage from the battery. The method furthercomprises conducting the supply current between the first node and asecond node via one or more transistors, thereby generating a voltagebetween the first node and the second node. The method further comprisesmeasuring, with a first circuit, the voltage generated between the firstnode and the second node. The method further comprises measuring, withthe first circuit, the supply voltage. The method further comprisesgenerating, with a second circuit, an estimate of the supply currentbased at least on the voltage measured between the first node and thesecond node and a resistance of the one or more transistors. The methodfurther comprises generating, with the second circuit, an estimate ofthe state of charge of the battery based at least on the measured supplyvoltage and the estimate of the supply current.

In another embodiment, a device for determining a state of a battery isdisclosed. The device comprises means for providing a resistance betweena first node and a second node. The providing means is configured toconduct a supply current between the first node and the second node,thereby generating a voltage between the first node and the second node.The device further comprises means for measuring the voltage generatedbetween the first node and the second node. The measuring means isconfigured to measure a supply voltage of the battery. The devicefurther comprises means for generating an estimate of the supply currentbased at least on the voltage measured between the first node and thesecond node and the resistance of the providing means. The generatingmeans is configured to generate an estimate of the state of charge ofthe battery based at least on the measured supply voltage and theestimate of the supply current.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a schematic block diagram illustrating a power systemincluding a battery gauge and a battery in accordance with variousembodiments described herein.

FIG. 2A is a schematic diagram illustrating one example embodiment of anisolation circuit of the battery gauge of FIG. 1.

FIG. 2B is a schematic diagram illustrating a circuit approximatelymodeling an operation of one example embodiment of an isolation circuitof the battery gauge of FIG. 1.

FIG. 3 is a schematic diagram of an example embodiment of a measurementcircuit of the battery gauge of FIG. 1.

FIG. 4 is process flow diagram of an example embodiment of a method forcalculating a state of charge of the battery of the power system of FIG.1.

FIG. 5 is process flow diagram of an example embodiment of a method fordetermining a compensated open circuit voltage of the battery of thepower system of FIG. 1.

FIG. 6 is plot of example embodiments of linear functions of state ofcharge versus battery open circuit voltage.

DETAILED DESCRIPTION

Embodiments relate to systems and methods for voltage-based fuelgauging. In one embodiment, the system measures a supply voltage of abattery during operation of the battery. Operation can includedischarging or charging the battery. Since the supply voltage depends onthe stored charge of the battery, the measured supply voltage can beused to estimate the remaining stored charge of the battery. Forexample, one or more functions can be used to map the measured supplyvoltage to the level of the remaining stored charge. The one or morefunctions can be derived based on experimental data generated fromvarious baseline conditions. One set of example baseline conditions mayinclude no loading on the battery and room temperature.

In one embodiment, the system corrects for various sources of errorsthat can occur during operation. This can happen because the operationof the battery may deviate away from the baseline conditions from whichthe relationship was derived. One example of a deviation that affectsthe relationship is a load current or charge current of the battery(“load level”). In addition, another example includes changes in theinternal temperature of the battery. Load level and temperature can eachaffect how the supply voltage of the battery is related to the level ofthe remaining charge of the battery. Various embodiments disclosedherein can reduce the errors caused by these effects by adjusting themeasured supply voltage with estimates of the off-baseline conditions.

In one specific example, the system estimates the load current of thebattery in order to compensate for load level effects. For example, thesystem can include an internal transistor used to sense the level of thesupply current that the battery is discharging or receiving. Theinternal transistor, being positioned between the battery and the systemto be powered, can be used to sense the level of the supply current byconducting the supply current and then by measuring the voltage dropacross the transistor generated by conducting the supply current. Byknowing the resistance provided by the transistor, the supply currentcan be estimated algebraically from the measured voltage of the internaltransistor. In turn, the estimated level of the load current can be usedto adjust the supply voltage measurement, and the adjusted supplyvoltage measurement can be mapped to the remaining charge of thebattery. In some embodiments, the resistance of the internal transistorcan be varied in order to trade off improved measurement resolution andreduced power consumption.

In another specific example, the system estimates the batterytemperature in order to compensate for temperature effects. For example,the system can include a circuit used to measure a voltage that isindicative of temperature of the battery. The estimated temperature canbe used to adjust the measurement of the supply voltage, and theadjusted supply voltage can be mapped the remaining charge of thebattery.

To further illustrate, FIG. 1 is a schematic block diagram illustratinga power system 100 including a battery gauge 102 and a battery 104 inaccordance with various embodiments described herein. The battery gauge102 can include an isolation circuit 106, a measurement circuit 108, acalculation and control circuit (“calculation circuit”) 110, and aprogrammable interface 112. The programmable interface 112 can includeone or more input registers 114, one or more battery-voltage registers116, and one or more state of charge registers 118. The battery 104 caninclude a voltage source V_(B) and an internal resistive element R_(T).

In the illustrated embodiment, the battery gauge 102 is operativelycoupled to the battery 104 at nodes ISO_B, BAT_SNS, and THR. The nodeISO_B can receive a supply voltage (e.g., manifesting as the voltageV_(ISO) _(—) _(B)) and supply current I_(BAT) from the battery 104 ifthe battery 104 is discharging. Additionally or alternatively, the nodeISO_B can provide a charging voltage and a charging current to thebattery 104 if the battery 104 is recharging. The node BAT_SNS canreceive a supply voltage (e.g., manifesting as the voltage V_(BAT) _(—)_(SNS)) from the battery 104 for voltage sensing. In some embodiments,the node BAT_SNS does not draw a substantial current. The node THR canreceive temperature-related measurements (e.g., manifesting as thevoltage V_(THR)) from the battery. In one embodiment, the node THRreceives negative temperature coefficient (NTC) information from abattery's thermistor or temperature sensor.

The isolation circuit 106 of the battery gauge 102 is operativelycoupled between nodes ISO_S and ISO_B of the battery gauge 102. The nodeISO_S can provide a supply voltage (e.g., manifesting as the voltageV_(ISO) _(—) _(S)) and a supply current I_(BAT) from the battery 104 ifthe battery 104 is discharging. Additionally or alternatively, the nodeISO_S can receive a charging voltage and a charging current to thebattery 104 if the battery 104 is recharging. The isolation circuit 106can serve a current sensing circuit disposed between the battery 104 andan external system (not shown).

The measurement circuit 108 of the battery gauge 102 is operativelycoupled to the nodes ISO_S, BAT_SNS, and THR of the battery gauge 102.In some embodiments, the measurement circuit 108 can be coupled to thenode ISO_B in addition to, or in alternative to, node BAT_SNS. Thecalculation circuit 110 of the battery gauge 102 is operatively coupledto the isolation circuit 106 and to the measurement circuit 108. Theprogrammable interface 112 of the battery gauge 102 is operativelycoupled to the calculation circuit 110.

In operation, the battery gauge 102 can be configured to generate anestimate of the state of charge of the battery 104. The term state ofcharge as used herein can include the amount of charge remaining in thebattery and can be expressed as a percentage. For example, a state ofcharge of 60% indicates that the battery is storing 60% of its capacity.

The node BAT_SNS can be configured to receive at least a portion of thesupply voltage V_(B) from the battery 104, which can generate ameasurement V_(BAT) _(—) _(SNS). The measurement V_(BAT) _(—) _(SNS) canbe at least partially indicative of the state of charge of the battery104. Accordingly, the battery gauge 102 can be configured to utilize themeasurement V_(BAT) _(—) _(SNS) for generating an estimate of the stateof charge, as will be described below in greater detail in connectionwith FIGS. 4-6.

Additionally or alternatively, the battery gauge 102 can be configuredto conduct a supply current I_(BAT) to and/or from the battery 104. Forexample, if the battery 104 is to supply power to an external system,the supply current I_(BAT) is carried from the node ISO_B to the nodeISO_S. Moreover, if the battery 104 is to receive power, the supplycurrent I_(BAT) is carried from the node ISO_S to the node ISO_B.

When the battery gauge 102 conducts the supply current I_(BAT) acrossthe nodes ISO_S and ISO_B, the battery gauge 102 can be configured togenerate a voltage V_(ISO) _(—) _(SB) across the nodes IOS_S and ISO_Bdue to a resistance between those nodes. Accordingly, the battery gauge102 can be configured to generate an estimate of the supply currentI_(BAT) based on the voltage V_(ISO) _(—) _(SB) and the resistanceprovided between the nodes ISO_S and ISO_B, as will be described belowin greater detail in connection with FIGS. 2A, 2B, and 5.

In one aspect described herein, estimating the supply current I_(BAT)can be used to improve the estimate of the state of charge of thebattery 104. Variations in the supply current I_(BAT) can affect therelationship between the measurement V_(BAT) _(—) _(SNS) and the stateof charge of the battery 104. In one embodiment the relationship betweenthe measurement V_(BAT) _(—) _(SNS) and the state of charge of thebattery 104 can be predetermined based on a baseline value of the loadlevel (e.g., one baseline can correspond to an open circuit voltage ofthe battery 104). If the battery 104, for example, supplies power to theexternal system, the actual relationship between the measurement V_(BAT)_(—) _(SNS) and the state of charge may vary from the predeterminedrelationship that was derived from the baseline conditions. Accordingly,to improve the accuracy of the estimate of the state of charge duringoperation, the battery gauge 102 can generate an estimate of the supplycurrent I_(BAT) to compensate for the load level on the battery 104during operation.

Additionally or alternatively, the battery gauge 102 can be configuredto measure or sense a characteristic of the battery 104 that isindicative of internal temperature of the battery 104. For example, theillustrated battery gauge 102 is operatively coupled to the resistiveelement R_(T) of the battery 104 at the node THR for receiving a voltageV_(THR). The resistive element R_(T) can have a resistance that changeswith the internal temperature of the battery 104. For example, theresistance of the resistive element R_(T) can increase as thetemperature of the battery 104 decreases. Moreover, the resistance ofthe resistive element R_(T) can decrease as the temperature of thebattery 104 increases. Accordingly, the battery gauge 102 can estimatethe temperature of the battery 104 based on the voltage V_(THR) and thecurrent I_(THR), as will be discussed in greater detail in connectionwith FIGS. 3-5.

In one aspect described herein, estimating the temperature of thebattery 104 can be used to improve the estimate of the state of chargeof the battery 104. For example, variations in the battery temperaturecan affect the relationship between the measurement V_(BAT) _(—) _(SNS)and the state of charge of the battery 104. For the purpose ofillustration, in one embodiment the relationship between the measurementV_(BAT) _(—) _(SNS) and the state of charge of the battery 104 can bepredetermined based on a baseline value of the temperature of thebattery 104. Accordingly, if during operation, the temperature of thebattery 104 varies, the relationship between the measurement V_(BAT)_(—) _(SNS) and the state of charge may vary as a result. Accordingly,to improve the accuracy of the estimate of the state of charge duringoperation, the battery gauge 102 can use an estimate of the temperatureof the battery 104 to compensate for temperature variations and/or offbaseline conditions during operation.

The isolation circuit 106 of the battery gauge 102 can be configured toconduct the supply current I_(BAT) between the battery 104 and theexternal system. In one embodiment the isolation circuit 106 can includeone or more transistors coupled between the nodes ISO_S and ISO_B.Accordingly, the isolation circuit 106 can provide a resistance (e.g.,the “on resistance” between the sources and the drains of thetransistors) between the nodes ISO_S and ISO_B. If the isolation circuit106 conducts the supply current I_(BAT) between the nodes ISO_S andISO_B, a voltage V_(ISO) _(—) _(SB) can be generated between the nodesISO_S and ISO_B.

In one embodiment, the isolation circuit 106 can be configured toprovide a selectable resistance between the nodes ISO_S and ISO_B. Theselection of the resistance of the isolation circuit 106 can be selecteddynamically during operation, for example, based on the magnitude of thesupply current I_(BAT) or the voltage V_(ISO) _(—) _(SB). For instance,the isolation circuit 106 can adjust the resistance between the nodesISO_S and ISO_B based on comparing one or more of the magnitude of thesupply current I_(BAT) or the voltage V_(ISO) _(—) _(SB) tocorresponding predetermined thresholds. In another embodiment, theselection of the resistance of the isolation circuit 106 is determinedoffline based on a setting (e.g., data received by the programmableinterface 112) of the battery gauge 102. As such, the resistance of theisolation circuit 106 can be determined during an initialization processby retrieving data from the programmable interface 112 and then settingthe resistance in accordance with the data. In one embodiment, thethreshold is based on the battery 104.

In one example aspect of some embodiments described herein, providing aselectable resistance between the nodes ISO_S and ISO_B can improve thequality of the measurements V_(ISO) _(—) _(SB), for example, if V_(ISO)_(—) _(SB) is relatively small (e.g., smaller than a threshold). Forexample, relatively small values of the voltage V_(ISO) _(—) _(SB) canoccur if the magnitude of the supply current I_(BAT) becomes relativelysmall (e.g., due to the state of charge, loading, and the likeconditions of the battery 104). Small values of the voltage V_(ISO) _(—)_(SB) can be difficult to measure effectively due to issues ofmeasurement precision, sensor resolution, signal-to-noise ratio, and thelike measurement issues. Accordingly, some embodiments of the isolationcircuit 106 can be configured to the select the resistance of theisolation circuit 106 in a way that generates the voltage V_(ISO) _(—)_(SB) at a level that can be effectively measured.

In another example aspect of some embodiments described herein,providing a selectable resistance between the nodes ISO_S and ISO_B canreduce power consumption of the battery gauge 102, for example, ifV_(ISO) _(—) _(SB) is relatively large. Relatively large values of thevoltage V_(ISO) _(—) _(SB) can occur if the magnitude of the supplycurrent I_(BAT) becomes relatively large (e.g., because of the state ofcharge, loading, and the like conditions of the battery 104). Largevalues of the voltage V_(ISO) _(—) _(SB) can consume substantially morepower than necessary. Accordingly, some embodiments of the isolationcircuit 106 can be configured to select the resistance provided by theisolation circuit 106 in a way that generates the voltage V_(ISO) _(—)_(SB) to reduce power consumption. For example, the isolation circuit106 can be configured to reduce the resistance of the isolation circuit106 if at least one of the supply current I_(BAT) or the voltage V_(ISO)_(—) _(SB) is greater than some predetermined threshold.

The isolation circuit 106 will be described in greater detail later inconnection with FIGS. 2A and 2B.

The measurement circuit 108 of the battery gauge 102 can be configuredto measure the voltage generated between the nodes ISO_S and ISO_B. Forexample, the measurement circuit 108 can have a first end operativelycoupled to the node ISO_S for sensing V_(ISO) _(—) _(S) and a second endoperatively coupled to the node ISO_B for sensing the voltage V_(ISO)_(—) _(B). In one embodiment, the measurement circuit 108 can beconfigured to sense the voltage V_(ISO) _(—) _(SB) for a fixed durationperiodically.

In one embodiment, the measurement circuit 108 can be configured tomeasure the supply voltage V_(BAT) _(—) _(SNS). For example, themeasurement circuit 108 can have a first end operatively coupled to thenode BAT_SNS (or ISO_B) for sensing V_(BAT) _(—) _(SNS) and a second endoperatively coupled to a reference node, such as ground. In oneembodiment, the measurement circuit 108 can be configured to sense thevoltage V_(BAT) _(—) _(SNS) for a fixed duration periodically.Additionally, the measurement circuit 108 can be configured to sense thevoltages V_(ISO) _(—) _(SB) and V_(BAT) _(—) _(SNS) simultaneously or atseparate times.

In another embodiment, the measurement circuit 108 can be configured tomeasure the voltage V_(THR) of the battery 104. As stated, the voltageV_(THR) is indicative of a temperature characteristic of the battery104. In one embodiment, the measurement circuit 108 is configured tosense the voltage V_(THR) for a fixed duration periodically.Additionally, the measurement circuit 108 can be configured to sense thevoltages V_(ISO) _(—) _(SB), V_(BAT) _(—) _(SNS), V_(THR) simultaneouslyor at separate times.

The measurement circuit 108 will be described in further detail later inconnection with FIG. 3.

The calculation circuit 110 of the battery gauge 102 can be configuredto receive one or more measurements of V_(ISO) _(—) _(SB), V_(BAT) _(—)_(SNS), or V_(THR) as inputs and to generate an estimate of the state ofcharge of the battery 104 as an output. For example, the calculationcircuit 110 can generate the state of charge based on receiving, fromthe measurement circuit 108, of one or more measurements of V_(ISO) _(—)_(SB), V_(BAT) _(—) _(SNS), or V_(THR). The state of charge can begenerated based on a relationship between the state of charge and themeasurements V_(ISO) _(—) _(SB), V_(BAT) _(—) _(SNS), or V_(THR). Thecalculation circuit can correspond to an application specific integratedcircuit (ASIC), a controller, a programmable logic device (PLD), logiccircuit, and/or a combination of such analog or digital electronics

In one embodiment, the relationship can be approximated by one or morelinear functions (e.g., in accordance to a piecewise linear function).For example, the state of charge can be based on one or more linearfunctions that relate a supply voltage to the state of charge of thebattery 104 at a baseline load level (e.g., an open circuit voltageV_(OCS)) and at a baseline temperature (e.g., room temperature). Forexample, the voltage V_(BAT) _(—) _(SNS) can be used as an approximationto the open circuit baseline voltage. In alternative embodiments, one ormore second-order or higher polynomials or other types of non-linearfunctions may be used instead of linear functions to approximate therelationship of the supply voltage to the state of charge of the battery104 at the baseline load level and at the baseline temperature.

In one embodiment, the calculation circuit 110 can be configured toretrieve data from the programmable interface 112 that determine therelationship between the supply voltage of the battery 104 to its stateof charge. For example, the calculation circuit may retrieve a pluralityof predetermined supply voltages corresponding to certain state ofcharge values. In one embodiment, the calculation circuit 112 retrievesfrom the a data register of the programmable interface 112 three valuesV_(BAT10), V_(BAT60), and V_(BAT90) that correspond to the open circuitvalues V_(OSC) that are associated with 10% state of charge, 60% stateof charge, and 90% state of charge, respectively. One skilled in the artwould appreciate that more or less values can be used. For example, inone embodiment, at least a 10-point table of battery voltage vs. stateof charge is stored in the input registers 114. The measured or sensedbattery V_(BAT) _(—) _(SNS) (or compensated open circuit voltage V_(OCS)as described below) can be compared to the retrieved data to calculateor estimate the current state of charge, for example by linearinterpolation or using linear functions. For example, the calculationcircuit 110 can include combinatorial logic to calculate the state ofcharge based on the measured or sensed supply voltage V_(BAT) _(—)_(SNS) and the retrieved data from the programmable interface 112.

During operation, the voltage V_(BAT) _(—) _(SNS) may not correspond tothe baseline voltage, for example, due to an off-baseline loading on thebattery 104, such as loading on the battery 104 or changes in thebattery temperature. Accordingly, the calculation circuit 110 can“adjust” or “compensate” V_(BAT) _(—) _(SNS) to estimate the baselinevoltage (e.g., by translating the voltage V_(BAT) _(—) _(SNS) to theopen circuit voltage V_(OCS)) by estimating the load current based onthe voltage V_(ISO) _(—) _(SB) and the resistance of the isolationcircuit 106. One example method for adjusting the battery supplymeasurement V_(BAT) _(—) _(SNS) based on the load current is describedis described in greater detail later in connection with FIG. 5 and, inparticular, Equation 4.

Additionally or alternatively, during operation, the temperature of thebattery 104 may not correspond to the baseline temperature, for example,due to the effects of discharging or charging the battery 104. In oneembodiment, the measurement circuit 108 can be configured to measure thevoltage VTHR and translate that voltage reading to a battery temperaturecoefficient T_(CBAT). For example, the battery temperature coefficientT_(CBAT) can be determined from the voltage V_(THR) based on NTC datastored in the input registers 118 of the programmable interface 112. TheNTC data can include a table of battery temperature coefficient T_(CBAT)vs. voltage V_(THR). Accordingly, the calculation circuit 110 can“adjust” V_(BAT) _(—) _(SNS) for use as the baseline voltage byestimating the temperature of the battery 104 based on the voltageV_(THR). One example method for adjusting the battery supply measurementV_(BAT) _(—) _(SNS) based on the temperature is described is describedin greater detail later in connection with FIG. 5 and, in particular,Equation 4.

In some embodiments the calculation circuit 110 can be configured tocontrol the isolation circuit 106. For example, based at least on one ofthe load current I_(B) or the voltage V_(ISO) _(—) _(SB), thecalculation circuit 110 can generate a control signal V_(ISO) to selectthe resistance of the isolation circuit 106, for instance, to improvethe measurements of V_(ISO) _(—) _(SB) and/or to reduce powerconsumption of the isolation circuit 106. In another embodiment, thecalculation circuit 110 can retrieve data from the programmableinterface 112. The data can be indicative of various operationparameters, including a selected resistance of the isolation circuit106. Additionally or alternatively, the operation parameters can includeminimum and/or maximum thresholds of at least one of the load currentI_(BAT) or voltage V_(ISO) _(—) _(SB). The thresholds can be used todetermine the selection of the isolation circuit 106. For example, ifthe load current I_(BAT) or voltage V_(ISO) _(—) _(SB) is below aminimum threshold, the calculation circuit 110 can be configured toincrease the resistance of the isolation circuit 106. As anotherexample, if the load current or voltage V_(ISO) _(—) _(SB) is above amaximum threshold, the calculation circuit 110 can be configured todecrease the resistance of the isolation circuit 106.

The programmable interface 112 of the battery gauge 102 can beconfigured to receive the estimate of the state of charge as an inputsand to provide the estimate of the state of charge as an output. Forexample, the programmable interface 112 can receive the estimate of thestate of charge from the calculation circuit 110 and store the estimatein the state of charge registers 118. Examples of the state of chargeregisters 118 include data registers and any other applicable datastorage circuits or devices. The programmable interface 112, in someembodiments, can provide an interface for external devices to access theestimate of the state of charge. For example, an external controller(not shown) can access the estimate of the state of charge register 118to determine a loading level on the battery 104 or to control a chargingprocess on the battery 104. In one embodiment, the programmableinterface 112 can correspond to any suitable interface includingregisters and a multimaster serial single-ended computer bus, such as anInter-Integrated Circuit (I²C) interface.

In addition, some embodiments of the programmable interface 112 can beconfigured to store the measurements of various voltages (e.g., V_(BAT)_(—) _(SNS), V_(ISO) _(—) _(SB), and/or V_(THR)). For example, theprogrammable interface 112 can be configured to receive measurementsfrom the calculation circuit 110 and to store those measurements in thebattery voltages register 116. Storing the measurements can aid in theprocess of estimate the state of charge. For example the measurementcircuit 108 can be configured to perform measurements sequentially. Inthis case, the measurements can be stored in the battery voltagesregister 116 until they are used to generate the estimate of the stateof charge. Additionally, the programmable interface 112 can provide themeasurements to an external device to perform various ancillary and/orindependent functions.

In addition, some embodiments of the programmable interface 112 can beconfigured to store various inputs to the battery gauge 102. As stated,one example input includes data used to determine the resistance of theisolation circuit 106. It will be appreciated that any suitable inputcan be stored in the input registers 114, such data related to batterycharacteristics, for example, but not limited to, the internalresistance of the batters, voltages used to determine the relationshipbetween the battery supply voltage and the state of charge (for example,the values of the voltages V_(BAT10), V_(BAT60), and V_(BAT90)), batterychemistry information, and NTC data.

In some embodiments, the isolation circuit 106, the measurement circuit108, and the calculation circuit 110 can form at least part of amonolithic integrated circuit. For example, the one or more transistorsof the isolation circuit 106 can be arranged internally to the batterygauge 102. The nodes ISO_S, ISO_B, BAT_SNS, and THR each can correspondto a physical pin, a pad, a port, a lead, a terminal, a contact, aconnector, or a like node of the integrated circuit of the fuel gauge102. In one embodiment, the integrated circuit of the battery gauge 102can be configured to charge the battery 104 by conducting a chargingcurrent from the second node to the first node via the one or moretransistors.

The one or more transistors of the isolation circuit 106 beinginternal—opposed to external resistors/transistors—can reduce powerconsumption of the battery gauge 102. Additionally, integrating the oneor more transistors of the isolation circuit 106 and to the integratedcircuit of the fuel gauge 102 allows the fuel gauge 102 to effectivelyand/or efficiently adjust the resistance of the isolation circuit 106.

FIG. 2A is a schematic diagram illustrating one example embodiment of anisolation circuit subsystem 200A of the power system 100 of FIG. 1. Theisolation circuit subsystem 200A includes the isolation circuit 106 ofthe fuel gauge 102 operatively coupled to the nodes ISO_S and ISO_B. Thebattery 104 includes a power supply approximately modeled by a voltagesource V_(BAT) and an internal resistor R_(IN). The illustrated voltagesource V_(BAT) and the internal resistor R_(IN) represent an approximatemodel of the behavior of the battery 104. As such, these components donot necessarily exist or do not necessarily correspond to actual lumpedphysical elements. The isolation circuit can include one or moretransistors, such as field effect transistors (FETs) 206-1, . . . ,206-N.

As stated previously above in connection with FIG. 1, the battery 104can be configured to provide a supply voltage V_(ISO) _(—) _(B) and asupply current I_(BAT) as outputs. Because the battery 104 includes aninternal resistance represented by R_(IN), the supply voltage V_(ISO)_(—) _(B) can be different (for example, less than) the voltage sourceV_(BAT). As will be described in greater detail below, this loadinglevel effect can detrimentally affect the estimation of the state ofcharge of the battery 104 if it is not compensated for.

The battery gauge 102 can be configured to receive the supply voltageV_(ISO) _(—) _(B) and the supply current I_(BAT) is inputs at the nodeISO_B. In addition, the isolation circuit 106 can be configured toreceive the supply current I_(BAT) as an input and to provide the supplycurrent I_(BAT) at the node ISO_S as an output.

The FETs 206-1, . . . , 206-N can be arranged in parallel across thenodes ISO_S and ISO_B. For example, each of the FETs 206-1, . . . ,206-N can correspond to an N-channel MOSFET (e.g., an enhancement modeMOSFET) having a source operatively coupled to the node ISO_S and adrain operatively coupled to ISO_B. In addition each of the FETs 206-1,. . . , 206-N includes a gate to receive a control (e.g.,V_(ISO1)-V_(ISON)). For example, the control signals V_(ISO1)-V_(ISON)can be provided by the calculation circuit 110 of FIG. 1. In oneembodiment, two or more of the control signals V_(ISO1)-V_(ISON) can beset independently to control the number of transistors that are in an ONstate and capable of conducting substantial current. The ON state cancorrespond to the linear region of operation and/or the saturationregion of operation. Accordingly, the control signals V_(ISO1)-V_(ISON)can determine the number of FETs 206-1, . . . , 206-N that are activatedand/or can change the resistance that an individual FET provides whileoperating in the linear region of operation.

The FETs 206-1, . . . , 206-N can correspond to insulated gatefield-effect transistors, such as MOSFETs. However, it will beunderstood that a gate can be made from materials other than metals,such as polysilicon, and an insulation layer can be made out ofmaterials other than silicon oxide, such as a high k dielectric. It willalso be understood that transistors 206-1, . . . , 206-N can havevarious structural types other than MOSFETs, including, but not limitedto, BJT, JFET, IGFET, MESFET, pHEMT, HBT, and the like transistorstructural types. Further, the transistors 206-1, . . . , 206-N can alsohave various polarities, such as N-type, P-type, NPN-type, and PNP-type;and can include various semiconductor materials, such as GaAs, SiGe, andthe like.

Turning momentarily to FIG. 2B, a schematic diagram is shownillustrating a circuit 200B that approximately models an operation of anexample embodiment of an isolation circuit 106 of the battery gauge 102of FIG. 1. Elements common to the schematics of FIGS. 2A and 2B sharecommon reference indicia, and only differences between the schematicsare described herein for the sake of brevity.

The fuel gauge 102 includes an equivalent on-resistor R_(ON) that servesto approximately model an example equivalent resistance provided by theisolation circuit 106 of FIG. 2A. The on-resistor R_(ON) has a first endoperatively coupled to the node ISO_B to receive the supply currentI_(BAT) as an input, and has a second and operatively coupled to thenode ISO_S to provide the supply current I_(BAT) as an output. In otherwords, the on-resistor R_(ON) can be configured to carry the supplycurrent I_(BAT) between the nodes ISO_S and ISO_B.

The resistance of the on-resistor R_(ON) can be determined based on thestates of the one or more transistors of the isolation circuit 106 ofFIG. 2A. For example, the resistance of the on-resistor R_(ON) candecrease as the number of transistors coupled between the nodes ISO_Sand ISO_B is activated. For another example, the resistance of theon-resistor R_(ON) can be modulated based on the control signalsV_(ISO1)-V_(ISON) of FIG. 2A biasing one or more transistors (e.g., FETs206-1, . . . , 206-N) operating in the linear region of operation. Asyet another example, the resistance of the on-resistor R_(ON) can bevaried by switching in and out transistors having different sizes (forexample, different channel widths). Accordingly, the resistance of theon-resistor R_(ON) can be adjusted to increase or decrease the voltagebetween ISO_S and ISO_B generated by the supply current I_(BAT).

Returning to FIG. 2A, the resistance (corresponding to the on-resistanceR_(ON) of FIG. 2B) of the isolation circuit 106 can be adjusted in anyappropriate way. For example, as stated, the number of activatedtransistors can be selected to change the overall resistance of theisolation circuit 106. In another embodiment, the bias or the operatingpoint of one or more transistors can be changed in order to change tooverall resistance of the isolation circuit 106. For example, one ormore of the FETs 206-1, . . . , 206-N can operate in the “linearregion,” “triode region,” or “ohmic mode” by selection of the gatevoltages V_(ISO1), . . . , V_(ISON), and the individual resistance ofthese FETs can be adjusted by adjusting the respective gate voltagesV_(ISO1)-V_(ISON). In another embodiment, the plurality of FETs 206-1, .. . , 206-N can each provide a different on-resistance value based onthe sizing of the FETs 206-1, . . . , 206-N, and the resistance of theisolation circuit 106 can be changed by activating the FET with sizethat yields the desired resistance and deactivating the remaining FETs.However, any other suitable method can be selected, such as varying the“effective” gate width or channel width of the transistors by fieldeffects or by activating/deactivating physical channels on theintegrated circuit. Moreover, the resistance of the isolation circuit106 can be selected during initialization and fixed during operation, orvaried dynamically based on the level of at least one of the supplycurrent I_(BAT) or the voltage V_(ISO) _(—) _(SB), as was discussedearlier in connection with FIG. 1. It will be appreciated that the oneor more transistors can be arranged in other applicable configurationsuitable to determine current flow and need not be arranged in theparallel configuration shown in FIG. 2A.

FIG. 3 is a schematic diagram of an example embodiment of a measurementcircuit 108 of the battery gauge 102 of FIG. 1. The illustratedmeasurement circuit 108 includes a multiplexer 302, analog-to-digitalconverter (ADC) 304, and a negative temperature coefficient (NTC) block306. In some embodiments, the NTC block 306 can include voltage sensingcircuitry, such as an ADC and digital logic circuitry.

The multiplexer 302 includes a first switch S1 that is configured toswitch between the nodes ISO_S and BAT_SNS in order to selectivelyprovide the voltage V_(ISO) _(—) _(S) or the voltage V_(BAT) _(—) _(SNS)as a first output. The multiplexer 302 further includes a second switchS2 that is configured to switch between the nodes ISO_B and GND toselectively provide V_(ISO) _(—) _(B) and V_(GND) as a second output.

The ADC 304 can be configured to receive the first and second outputs ofthe multiplexer 302, an oscillator voltage V_(OSC), and a referencevoltage V_(REF) as inputs and to provide various digital measurements asoutputs. For example, the ADC 304 can be configured to measure thevoltage V_(ISO) _(—) _(SB) by taking the difference between the firstand second outputs of the multiplexer 302 if the first switch S1 is setto couple with the node ISO_S and the second switch S2 is set to couplewith the node ISO_B. In addition, the ADC 304 can be configured tomeasure V_(BAT) _(—) _(SNS) by taking the difference between the firstand second outputs of the multiplexer 302 if the first switch S1 is setto couple with the node BAT_SNS and the second switch S2 is set tocouple with the node GND. The oscillator voltage V_(OSC) can serve toprovide a timing signal, such as a clock signal. The reference voltageV_(REF) can serve to provide quantization parameters, such asquantization levels, and to bias the ADC. In one specific embodiment,the ADC corresponds to a 12-bit ADC circuit. However, ADCs having anysuitable bit numbers can be used in view of cost, complexity, powerconsumptions, and other application specific considerations.

The NTC block 306 is configured to receive a voltage V_(THR) as an inputand configured to provide a battery temperature coefficient T_(CBAT) asan output. In one embodiment, the battery 104 can include a thermistor,which is a resistor with negative temperature coefficient, for providingthe voltage V_(THR). However, alternative embodiments can be providedtemperature information from other external sources. For example, amicrocontroller can read temperature information from an externaltemperature sensing circuit and can write the result to NTC block 306via an interface such as an I²C bus.

Accordingly, the NTC block 306 can generate the battery temperaturecoefficient T_(CBAT) based on receiving the voltage V_(THR) from thenode THR. As stated, the voltage V_(THR) is indicative of internaltemperature of the battery 104. Moreover, the battery temperaturecoefficient T_(CBAT) is based on the temperature of the battery 104.Accordingly, the NTC block 306 implements the mapping of the voltageV_(THR) to the battery temperature coefficient T_(CBAT). As stated, insome embodiments, the NTC block 306 can access the programmableinterface 112 to retrieve stored data related to mapping the sensedvoltage V_(THR) to the battery temperature coefficient T_(CBAT). In oneexample embodiment, the programmable interface 112 stores data relatedto pre-categorizing the voltage V_(THR) to the battery temperaturecoefficient T_(CBAT). In another embodiment, the data can include aplurality of V_(THR), T_(CBAT) pairs used for interpolating the measuredto V_(THR) to the battery temperature coefficient T_(CBAT). The mappingcan be implemented by using any suitable method, such as analog ordigital circuitry or general-purpose processor executing instructions(e.g., implementing a table lookup, interpolation, or the like mappingmethods).

FIG. 4 is process flow diagram of an example embodiment of a method 400for calculating a state of charge of a battery of the power system 100of FIG. 1. The method 400 can include a block 402 for measuring thebattery voltage V_(BAT) _(—) _(SNS). The measurement of the batteryvoltage V_(BAT) _(—) _(SNS) can correspond to an analog or digitalsignal. For instance, the battery voltage V_(BAT) _(—) _(SNS) can bemeasured or sensed at the node BAT_SNS of a fuel gauge by using ameasurement circuit, such as shown in the example of FIG. 1. In oneembodiment, an ADC can be used to measure V_(BAT) _(—) _(SNS) bydigitally sampling and taking the difference in voltages between thenodes BAT_SNS and GND, such as shown in the example of FIG. 3.

The method 400 can include a block 404 for measuring the voltage V_(ISO)_(—) _(SB) across an isolation circuit. The isolation circuit caninclude one or more transistors conducting a supply current I_(BAT) fromthe battery to an external system. The one or more transistors canprovide resistance that causes a voltage to be generated as the one ormore transistors conduct the supply current I_(BAT). The measurement ofthe voltage V_(ISO) _(—) _(SB) across the isolation circuit cancorrespond to an analog or digital signal. For instance, the voltageV_(ISO) _(—) _(SB) can be measured or sensed by measuring the voltagesat the nodes ISO_S and _(ISO) _(—) _(B) by using a measurement circuit,such as shown in the example of FIG. 1. In one embodiment, an ADC can beused to measure V_(ISO) _(—) _(SB) by digitally sampling and taking thedifference in voltages between the nodes ISO_S and ISO_B, such as shownin the example of FIG. 3.

The method 400 can include block 406 for determining a compensated opencircuit battery voltage V_(OCS). For example, the compensated opencircuit battery voltage V_(OCS) can be determined by adjusting thebattery voltage V_(BAT) _(—) _(SNS) based on the measured voltageV_(ISO) _(—) _(SB) of block 402. In addition, the compensated opencircuit battery voltage V_(OCS) can be determined by also adjusting thebattery voltage V_(BAT) _(—) _(SNS) based on the temperature of thebattery. As stated, the measured battery voltage V_(BAT) _(—) _(SNS) canbe adjusted to compensated for variations in battery loading levels andtemperature and to translate the measured battery voltage V_(BAT) _(—)_(SNS) to the “baseline” open circuit battery voltage. As stated, thestate of charge can be determined based on a relationship (such as oneor more equations) between, for example, the baseline open circuitbattery voltage. Accordingly, the measured battery voltage V_(BAT) _(—)_(SNS) should be adjusted to the baseline during operation in order touse the relationship effectively. In one embodiment, a calculationcircuit can be used to determine the compensated open circuit batteryvoltage V_(OCS), such as shown in the example of FIG. 1. Block 406 willbe described in greater detail later in connection with FIG. 5.

The method 400 can include block 408 for comparing the compensated opencircuit battery voltage V_(OCS) to a threshold or a range. This test canbe performed to account for the changes in the relationship between thecompensated open circuit voltage V_(OCS) and the state of charge of thebattery. In particular, it has been observed that the relationshipchanges as the state of charge changes. In particular, the sensitivityof the relationship of the state of charge to the compensated opencircuit voltage V_(OCS) varies with the state of charge. As a result,modeling the relationship between the state of charge and the opencircuit voltage V_(OCS) by a single function may be difficult todetermine, may not be effective due to modeling errors, or may bedifficult to implement because of the model's complexity andcomputational cost. Thus, to approximate the changes in therelationship, the relationship between the compensated open circuitbattery voltage and the state of charge can be approximately modeled bya piecewise linear equation. In other words, a plurality of linearequations are used to model the relationship. Linear equations can beevaluated with low computational costs. Moreover, accuracy can beimproved by using additional linear equations. At least one embodimentuses a piecewise linear function that has been determined throughexperimental measurements, as indicated by the curve of FIG. 6.

The particular linear function that is selected for a particularcalculation can depend on the state of charge. For example, the linearfunction to be used for determining the state of charge for a calculatedcompensated open circuit voltage V_(OCS) can be selected based ontesting whether the compensated open circuit voltage V_(OCS) is withinone of a number of ranges, wherein the ranges are based on pastmeasurements of the state of charge. For further example, in oneembodiment, the calculation circuit is configured to determine if thecompensated open circuit voltage V_(OCS) in the range of V_(BAT10) andV_(BAT60). As stated, V_(BAT10) is compensated open circuit voltageV_(OCS) determined experimentally to correspond to 10% state of chargeand V_(BAT60) is the open compensate voltage V_(OCS) determinedexperimentally to correspond to 60% state of charge. If the compensatedopen circuit voltage V_(OCS) is within that range, then a linear portionof the piecewise linear equation that corresponds to that range can beused to determine the state of charge based on the compensated opencircuit voltage V_(OCS). As stated, the piece-wise linear function canbe produce by curve fitting experimental data, and data characterizingthe piecewise linear function can be stored in the input registers 114of the programmable interface 112, as shown in FIG. 1.

In one example embodiment, the relationship between the compensated opencircuit battery voltage V_(OCS) and the state of charge can beapproximated by two linear functions over two separate domains. Forexample, the relationship between state of charge and the compensatedopen circuit voltage V_(OCS) can vary with value of the compensated opencircuit voltage V_(OCS). For instance, the relationship can beapproximated by a first linear function over the domain ofV_(OCS)<V_(BAT60), and can be approximated by a second liner functionover the domain V_(OCS)>V_(BAT60), where V_(BAT60) is the open circuitbattery voltage corresponding to 60% state of charge. In this case,V_(BAT60) can be selected as the threshold. In another example, therelationship can be approximated by a first linear function over thedomain or range of V_(BAT10)<V_(OCS)<V_(BAT60), and can be approximatedby a second liner function over the domain or range ofV_(BAT60)<V_(OCS)>V_(BAT90), where V_(BAT10) is the open circuit batteryvoltage corresponding to 10% state of charge and V_(BAT90) is the opencircuit battery voltage corresponding to 90% state of charge. In thiscase, the values V_(BAT10), V_(BAT60), and V_(BAT90) can be used asthree thresholds. Accordingly, in such an embodiment, if the testV_(OCS)<V_(BAT60) passes (and, if appropriate, V_(OCS)>V_(BAT10)), thenthe method proceeds to block 410. Otherwise, the method 400 continues toblock 412 (and, if appropriate, V_(OCS)<V_(BAT90)). In one embodiment, acalculation circuit can be used to test the compensated open circuitbattery voltage V_(OCS), such as shown in the example of FIG. 1.

The method 400 can include block 410 for calculating a state of chargeof the battery using the first equation if the condition of block 408 issatisfied. For instance, the calculation circuit can be configured togenerate the estimate of the state of charge based on the first linearrelationship if the adjusted open voltage measurement is less than apredetermined threshold. In one embodiment, the first linear functioncan correspond to the following equation:

$\begin{matrix}{{SoC} = {{\frac{{60\%} - {10\%}}{V_{{BAT}\; 60} - V_{{BAT}\; 10}}\left( {V_{OCS} - V_{{BAT}\; 10}} \right)} + {10\%}}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$

In Equation 1, the quantity V_(BAT10) can correspond to a constantrepresenting an open circuit battery voltage that corresponds to 10%state of charge. In one embodiment, the calculation circuit can be usedto evaluate the first equation, such as shown in the example of FIG. 1.

The method 400 can include block 412 for calculating a state of chargeof the battery using a second equation if the test of block 408 failed.For instance, the calculation circuit can be configured to generate theestimate of the state of charge based on the second linear relationshipif the adjusted open voltage measurement is greater than thepredetermined threshold. In one embodiment, the first linear functioncan correspond to the following equation:

$\begin{matrix}{{SoC} = {{\frac{{90\%} - {60\%}}{V_{{BAT}\; 90} - V_{{BAT}\; 60}}\left( {V_{OCS} - V_{{BAT}\; 60}} \right)} + {10\%}}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

In Equation 2, the quantity V_(BAT90) can correspond to a constantrepresenting an open circuit battery voltage that corresponds to 90%state of charge. In one embodiment, the calculation circuit can be usedto evaluate the second equation, such as shown in the example of FIG. 1.

The method 400 can include block 414 for providing the state of charge.In one embodiment, the calculation circuit can provide the estimate ofthe state of charge state of charge to a programmable interface, such asshown in the example of FIG. 1.

FIG. 5 is process flow diagram of an example embodiment of a method 406for determining a compensated open circuit voltage V_(OCS) of a batteryof the power system of FIG. 1. At block 502, the method 406 calculatesthe supply current I_(BAT) based on the isolation circuit voltageV_(ISO) _(—) _(SB). As stated, the isolation circuit voltage V_(ISO)_(—) _(SB) can be measured by measuring the voltages at the nodes ISO_Sand ISO_B of the battery gauge and based on the on-resistance R_(ON) ofthe isolation circuit. In particular, the supply current I_(BAT) can beestimated in accordance with the following equation:

I _(BAT)=(V _(ISO) _(—) _(B) −V _(ISO) _(—) _(S))÷R _(ON)  (Eq. 3)

In Equation 3, the voltages V_(ISO) _(—) _(B) and V_(ISO) _(—) _(S) canbe measured, as stated. The on-resistance R_(ON) can correspond to theresistance of the isolation circuit, which may be provided by aprogrammable interface or provided as a factory programmed value.

At block 504, the method 406 determines the battery temperaturecoefficient T_(CBAT). Battery temperature variations can negativelyimpact the accuracy of the fuel gauge reading. Accordingly, someembodiments estimate the battery temperature coefficient T_(CBAT) inorder to compensate for temperature variations. The battery temperaturecan be obtained via a voltage level V_(THR) of a NTC resistor (e.g.,R_(T) of FIG. 1) output inside the battery pack. The voltage V_(THR) canbe mapped to pre-characterized temperature coefficients so that thebattery internal resistance value can be adjusted to improve loadcompensation. The temperature coefficients can be obtained duringoperation by hardware or software implemented equations or look-uptables.

At block 506, the method 406 can determine the compensated open circuitvoltage V_(OCS) based on the measurement of the battery voltage V_(BAT)_(—) _(SNS), the estimated battery load current I_(BAT), and theestimated battery temperature coefficient T_(CBAT). In one embodiment,the compensated open circuit voltage V_(OCS) can be estimated inaccordance with the following equation:

V _(OCS) =V _(BAT) _(—) _(SNS) +R _(IN) ×T _(C) _(BAT) ×I _(BAT)  (Eq.4)

In equation for, the voltage V_(BAT) _(—) _(SNS) can be measured, asstated. The resistance RIN can correspond to the internal resistance ofthe battery, which may be provided by a programmable interface orprovided as a factory programmed value. The term R_(IN)×T_(C) _(BAT)×I_(BAT) can represent the adjustment made to the measured supplyvoltage.

FIG. 6 is plot 600 of example embodiments of linear functions of stateof charge versus battery open circuit voltage. The plot 600 illustratesthe state of charge of a battery as a function of battery open circuitvoltages for various temperatures. The battery state of charge isrepresented by the vertical axis. The battery open circuit voltage isrepresented by the horizontal axis. Lines 602, 604, and 606 representmeasurements of the state of charge at 0 C, 25 C, and 40 C,respectively. The line 608 is a piecewise linear function that has beengenerated to approximate the lines 602, 604, 608. As shown, line 608 hasa nonlinearity point when it has a state of charge of 60%. For thebattery open circuit voltages before this point, the line 608 is linearand that portion can represent the first linear equation. For thebattery open circuit voltages after this point, the line 608 is alsolinear and that portion can represent the second linear equation.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. A device to determine a state of a battery,the device comprising: first and second nodes, the first node beingconfigured to receive a supply current and a supply voltage from thebattery; one or more transistors configured to provide a resistancebetween the first and second node, the one or more transistors beingconfigured to conduct the supply current between the first node and thesecond node, thereby generating a voltage between the first node and thesecond node; a measurement circuit configured to measure the voltagegenerated between the first node and the second node, the measurementcircuit being further configured to measure the supply voltage; and acalculation circuit configured to: generate an estimate of the supplycurrent based at least on the voltage measured between the first nodeand the second node and the resistance of the one or more transistors;and generate an estimate of the state of charge of the battery based atleast on the measured supply voltage and the estimate of the supplycurrent.
 2. The device of claim 1, further comprising an integratedcircuit including the one or more transistors, the measurement circuit,and the calculation circuit.
 3. The device of claim 2, wherein theintegrated circuit is further configured to charge the battery byconducting a charging current from the second node to the first node viathe one or more transistors.
 4. The device of claim 1, wherein themeasurement circuit is further configured to measure a second voltage ofthe battery, the second voltage indicative of a temperaturecharacteristic of the battery, the calculation circuit being configuredto generate the estimate of the state of charge based at least furtheron the second voltage of the battery.
 5. The device of claim 4, whereinthe measurement circuit comprises a temperature monitoring circuitconfigured to generate an estimate of a temperature coefficient of thebattery based on the measured second voltage, the calculation circuitbeing configured to determine the state of charge based at least furtheron the estimate of the temperature coefficient.
 6. The device of claim5, wherein the calculation circuit is further configured to generate anadjusted voltage measurement based on the measured supply voltage, theestimate of the supply current, and the estimate of the temperaturecoefficient, the calculation circuit is further configured to generatethe estimate of the state of charge based on a first linear relationshipbetween the adjusted voltage measurement and the state of charge.
 7. Thedevice of claim 6, wherein the calculation circuit is further configureddetermine whether the adjusted voltage measurement is within a firstrange of a plurality of ranges of battery voltages associated withcorresponding state of charges, the calculation circuit being furtherconfigured to generate the estimate of the state of charge based on thefirst linear relationship if the calculation circuit determines that theadjusted voltage measurement is within the first range.
 8. The device ofclaim 7, wherein the plurality of ranges includes the first range and asecond range, the first range corresponding to a first baseline batteryvoltage and a second baseline battery voltage, the second rangecorresponding to the second baseline battery voltage and a thirdbaseline battery voltage, the first baseline battery voltagecorresponding to a first state of charge derived from experimental data,the second baseline battery voltage corresponding to a second state ofcharge derived from experimental data, the third baseline batteryvoltage corresponding to a third state of charge derived fromexperimental data.
 9. The device of claim 7, further comprising: a datastorage device configured to store data, the data including a pluralityof voltages indicative of at least the first range of the plurality ofranges, wherein the calculation circuit comprises a logic circuitconfigured to: retrieve the data from the data storage device; determinewhether the adjusted voltage measurement is within the first range basedon the data retrieved from the data storage device; and generate theestimate of the state of charge based on the first linear relationshipif the logic circuit determines that the adjusted voltage measurement iswithin the first range.
 10. The device of claim 1, wherein themeasurement circuit comprises an analog-to-digital converter (ADC), theADC configured to selectively measure the voltage between the first nodeand the second node, the ADC further configured to selectively measurethe supply voltage.
 11. The device of claim 1, wherein the one or moretransistors are configured to conduct the supply current with a variableamount of resistance.
 12. The device of claim 11, wherein the one ormore transistors include first and second transistors operativelycoupled in parallel between the first and second nodes, wherein thefirst and second transistors are configured to activate independently.13. The device of claim 12, wherein the second transistors is configuredto active when the supply current is less than a predeterminedthreshold.
 14. The device of claim 1, further comprising one or moredata registers configured to store the estimate of the state of charge.15. A method for determining a state of a battery, the methodcomprising: receiving, at a first node, a supply current and a supplyvoltage from the battery; conducting the supply current between thefirst node and a second node via one or more transistors, therebygenerating a voltage between the first node and the second node;measuring, with a first circuit, the voltage generated between the firstnode and the second node; measuring, with the first circuit, the supplyvoltage; generating, with a second circuit, an estimate of the supplycurrent based at least on the voltage measured between the first nodeand the second node and a resistance of the one or more transistors; andgenerating, with the second circuit, an estimate of the state of chargeof the battery based at least on the measured supply voltage and theestimate of the supply current.
 16. The method of claim 15, furthercomprising an integrated circuit including the one or more transistors,the first circuit, and the second circuit.
 17. The method of claim 16,further comprising charging the battery by conducting a charging currentfrom the second node to the first node via the one or more transistors.18. The method of claim 15, further comprising measuring a secondvoltage of the battery, the second voltage being indicative of atemperature characteristic of the battery, the generating the estimateof the state of charge based at least further on the second voltage ofthe battery.
 19. The method of claim 15, wherein the conducting thesupply current between the first node and a second node via one or moretransistors comprises conducting the supply current with a variableamount of resistance.
 20. A device for determining a state of a battery,the device comprising: means for providing a resistance between a firstnode and a second node, the providing means configured to conduct asupply current between the first node and the second node, therebygenerating a voltage between the first node and the second node; meansfor measuring the voltage generated between the first node and thesecond node, the measuring means configured to measure a supply voltageof the battery; and means for generating an estimate of the supplycurrent based at least on the voltage measured between the first nodeand the second node and the resistance of the providing means, thegenerating means configured to generate an estimate of the state ofcharge of the battery based at least on the measured supply voltage andthe estimate of the supply current.